1. Field of the Invention
The present invention relates to a color printing apparatus, and more particularly to a printing apparatus and method for printing color data useful in the multimedia processing for CAD (Computed Aided Design), CG (Computer Graphics), design, and color DTP (Desk Top Publishing) in the business, etc., at high resolution and high gradation.
2. Related Background Art
With the advent of intelligent work stations or personal computers in recent years, the environment in which the handling of characters, graphics or image data in full color is easily made has been prepared. As a result, color information has been utilized in a broad field for documents with color, OHP (Over Head Projector), slide, art, or design.
In this way, applications with color information on the host computer have been useful over the broad field. However, in recording the color information created on the host computer into the printing apparatus, it is conventionally common to rely on the utilization form of what is called a dumb printer or video printer of expanding characters, images and graphics into an image in accordance with the resolution of a recording apparatus, on the host side, using CPU power (process function) of the host computer, and then transferring the image to the color printer. This processing system has the feature of simplifying the mechanism on the printer side and performing many processes on the host side, but in handling the color information, it has a problem that it takes more time to make the communication due to a great amount of data thereof, resulting in significantly lower throughput.
On the other hand, in black-and-white printers, it is common to rely on a method, referred to as a page description language (hereinafter abbreviated as PDL) method, of creating the page image in such a way as to send characters, graphics and images as a language from the host side, interpreting the PDL language in the printer, and scan converting various types of information into a raster memory corresponding to the resolution of the printer. Color PDL printers to which this scan system is applied have recently come into wide use.
However, in the color PDL printers, a language architecture (structure) of conventional black-and-white PDL printers is followed, in which an operation such as SET, OR or XOR is performed bit by bit between the information (destination) already rendered for black-and-white or 1 bit information, and the information (source) of graphics, images and characters subsequently rendered. But in color printers, each of the color planes, e.g., RGB (red, green, blue) has a depth (e.g., 1, 2, 4, 8 bits), which is problematical in that if a conventional operation such as SET, OR or XOR is performed bit by bit, a desired color may not be obtained, whereby a logical operation function in view of the bit depth such as (Add, Sub, Max, Min, Blend), which is referred to as a color logical drawing, has been introduced.
However, the above color logical drawing had a problem on that because it was necessary to operate the information having color depth for as many as three or four planes, the processing was very costly.
Also, in the color PDL printers with the products bipolarized, that is, in the low price color printers represented by an ink jet or thermal transfer type, the page memory possesses one bit for each of four colors of YMCK, like the black-and-white printers. In making a color image or color character, or painting with color designation, the color gradation is falsely reproduced basically by dither, or an error diffusion method, to pursue the color accuracy, at the expense of resolution.
On the other hand, in high price color printers represented by a color LBP, multiple gradations/densities (e.g., 256 gradations for each color) are representable with one pixel for each of colors YMCK. In such a printing apparatus, the designated colors are directly held within the recording apparatus as the above pseudo-gradation processing is not required, and simply sent to a printer engine. However, in this recording apparatus, a page buffer for storing multi-value YMCK colors is required, wherein with a resolution of 300 DPI, a gradation of 8 bits for each color, and the maximum paper size of A4, the page memory required may be as large as 1M*4 (color)*8 (bit)=32 MB, resulting in very costly processing. Therefore, the latter can print a higher definition image, but is significantly more expensive than the former in the price of a physical printing apparatus and controller.